1. Field of the Invention
The present invention relates to a sheet feeder configured to separate, one by one, sheets from a plurality of sheets held by a sheet supply tray and to feed the separated sheets to a conveying path.
2. Related Art
Known copiers, scanners, printers, and multifunction apparatus combining copier, scanner, and printer functions include an ADF (automatic document feeder) that feeds a sheet from a sheet supply tray via a conveying path to a sheet ejection tray. Such a known ADF includes a feeder that separates held by a sheet supply tray and feeds the sheets to a conveying path successively.
For example, as shown in FIG. 14, a sheet feeder 91 included in a known ADF 90 is formed with a pickup-side chute portion 93 connected to a sheet supply tray 92 used for placing sheets thereon. The pickup-side chute portion 93 includes a pickup roller 94, a pickup-side nip member 95, a separation roller 96, and a separation nip member 97.
The pickup roller 94 is rotatably disposed on a lower guide surface of the pickup-side chute portion 93. On an upper guide surface of the pickup-side chute portion 93, which is an opposite position of the pickup roller 94, the pickup-side nip member 95 is disposed to make contact with and separate from the pickup roller 94, and is urged by a spring member, not shown, in contact with the pickup roller 94. Sheets set in the sheet supply tray 92 are urged by the pickup-side nip member 95 toward the pickup roller 94. A lowermost sheet, which is pressed in contact with the pickup roller 94, is subject to a rotation of the pickup roller 94, and then is fed in a sheet feeding direction.
The separation roller 96 is rotatably disposed on the lower guide surface of the pickup-side chute portion 93 at a predetermined distance away from the pickup roller 94 with respect to the sheet feeding direction. On the upper guide surface of the pickup-side chute portion 93, which is an opposite position of the separation roller 96, the separation nip member 97 is disposed to make contact with and separate from the separation roller 96, and is urged by a spring member (not shown) in contact with the separation roller 96. The sheet fed by the pickup roller 94 is nipped between the separation roller 96 and the separation nip member 97, subjected to the rotation of the separation roller 96, and is fed in the sheet feeding direction.
On a downstream side from the pickup-side chute portion 93, a conveying path 98 having laterally-facing U shape is formed. The sheet supplied from the sheet supply tray 92 is fed along the conveying path 98 by conveying roller 99 and pinch rollers 100 disposed thereon. During the feeding process, the sheet is guided by a guide member 101 onto a platen glass 102, and an image scanner 103 reads an image of the sheet passing on the platen glass 102. After image reading, the sheet is ejected from the conveying path 98 to a sheet ejection tray 104.
To feed a sheet in the sheet feeding direction upon the rotation of the pickup roller 94 as described above, the sheet is inserted with its leading end inserted inward more than a nip position between the pickup roller 94 and the pickup-side nip member 95 when set in the sheet supply tray 92. If the pickup roller 94 and the pickup-side nip member 95 are in contact with each other, the user pushes the sheet to the nip position by withdrawing the pickup-side nip member 95, and further pushes the nipped sheet by causing the double sides to slide with respect to the pickup roller 94 and the pickup-side nip member 95.
However, if the user feels resistance at the nip position between the pickup roller 94 and the pickup-side nip member 95 during the sheet insertion, the user may mistake the position for an insertion limit position, and may finish inserting the sheet. In this case, the sheet is not completely set, and the sheet cannot be fed by the pickup roller 94. In addition, to set a plurality of sheets, the sheet may be bent at the nip position between the pickup roller 94 and the pickup-side nip member 95 because the plurality of sheets are flexible.
To address this issue, in another known ADF, when a plurality of sheets are set, either the pickup roller 94 or the pickup-side nip member 95 is withdrawn to provide a gap between the pickup roller 94 and the pickup side nip member 95, such that the sheet may be inserted. For example, as shown in FIG. 14, the pickup roller 94 protrudes or withdraws with respect to a guide surface of the pickup-side chute portion 93, and the pickup roller 94 is operated by a solenoid (not shown). In a situation when the sheet feeder 91 is not active, the pickup roller 94 is withdrawn to form a gap between the pickup roller 94 and the pickup-side nip member 95, so that insertion and removal of a plurality of sheets is facilitated. To feed the sheet after being set, the pickup roller 94 is protruded and the sheet are nipped between the pickup roller 94 and the pickup-side nip member 95. Then, upon the rotation of the pickup roller 94, the lowermost sheet is fed in the sheet feeding direction.
However, this known ADF increases the number of parts and increases the complexity of manufacturing the ADF, which increases the size of the ADF and the cost of manufacturing the ADF.